The present invention generally relates to blister packaging apparatuses, and more particularly to a blister packaging apparatus which can use a packaging material such as a polypropylene sheet.
A blister package which utilizes blisters formed in a thermoplastic resin sheet is popularly used in packaging medicine tablets, medicine capsules, confectioneries, medical supplies, mechanical parts and the like. In such a blister package, a slit (half-cut line) is formed in the sheet for every one or a plurality of blisters, so as to facilitate the separation of the blisters.
Conventionally, a polyvinyl chloride sheet (hereinafter simply referred to as a PVC sheet) is used for the sheet of the blister package. However, there are problems in that chlorine gas is generated during a thermal process and the moistureproofing provided by the PVC sheet is insufficient. For this reason, the use of a polypropylene sheet for the blister package is recently being considered. However, the polypropylene sheet is more resilient than the PVC sheet, and it is difficult for a blade to cut into the resilient polypropylene sheet to form the half-cut line.
The half-cut line is conventionally formed by pushing an elongated blade, for example, against the sheet so as to cut into the sheet. This method is effective with respect to the PVC sheet, but in the case of the polypropylene sheet, the elongated blade does not satisfactorily cut into the polypropylene sheet and it is impossible to form a desired half-cut line.
There is also a conventional method of moving a blade having a triangular tip along a direction parallel to a surface of the sheet so as to form the half-cut line. According to this method, it is possible to form the half-cut line in the polypropylene sheet. However, because of the triangular shape of the blade, there actually are the following problems.
Firstly, the serviceable life of the blade is short because the tip end of the blade is sharp and the blade wears out quickly because of the large resistance due to friction during the half-cutting.
Secondly, it is difficult to smoothly carry out the half-cutting due to the vibration of the blade caused by the sharp tip end of the blade, the large resistance due to friction during the half-cutting and the abrupt resistance due to friction acting on the blade when the blade cuts into the sheet.
Thirdly, it is impossible to carry out the half-cutting at a high speed due to the large vibration of the blade.
Fourthly, when the blade wears out due to the friction, it is necessary to remove the worn blade, mount a new blade and then adjust the half-cutting quantity of the new blade, and the maintenance is troublesome to carry out.
On the other hand, the blister is formed by drawing a corresponding portion of the sheet into a concave pocket in a drum surface by suction, and a top portion of the blister tends to become thinner than other portions of the blister. Furthermore, since a suction hole is located at a bottom surface of the concave pocket, that is, at a position confronting the top portion of the blister, the thin top portion of the blister is partially sucked into the suction hole and a small conical projection is formed thereby on the top portion of the blister.
The small conical projection on the top portion of the blister is not only undesirable from the point of view of the external appearance of the blister package, but also causes problems when stacking such blister packages on top of one another. In other words, the blister packages are often stacked, but when the small conical projection is formed on the top portion of the blister, the small conical projection of a lower blister package may make contact with and damage a bottom of the blister of an upper blister package, because the bottom of the blister is often simply covered by an aluminum foil. The damage to the aluminum foil covering the bottom of the blister is undesirable from the point of view of quality control, especially in the case where medicine tablets and the like are contained in the blister package.